1. Field of the Invention
The present invention relates to an image processing apparatus and conversion method thereof for converting image data that has been scanned by a scanner into a vector format.
2. Description of the Related Art
It has recently become common to scan paper documents using a scanner and store the scanned documents in digitized form. A document scanned by a scanner is stored, for example, as image data in bitmap format.
The bitmap format expresses characters as a group of dots (pixels), and thus it is not necessary to perform complex calculations when displaying or printing those characters. However, the bitmap format has a disadvantage in that “jaggies” (stair-like artifacts) may be noticeably visible in the contours of the characters displayed or printed depending on the resolution of the apparatus that outputs (displays or prints) the characters (the output apparatus).
A process called “outlining” has therefore been conventionally performed so as to convert bitmap images into vector font images (vector images).
In a vector image, a character is reproduced by forming contour lines by approximating the contours of the character to straight lines and curved lines and then filling in the regions surrounded by those contour lines, a process that makes jaggies less apparent. Furthermore, because the outputted product does not depend on the resolution of the output apparatus, the image quality of character portions can be stabilized easily even if the output apparatus changes. However, it is necessary to increase the number of points used to reproduce the contours of a character (contour points) in order to express the character as accurately and smoothly as possible in a vector image. As a result, maintaining the image quality of character portions significantly increases the amount of data.
An image processing apparatus has been proposed as conventional technology regarding vector images (JP 2007-129557A).
According to the image processing apparatus, image data obtained by scanning a document is divided according to attributes such as character size, font, color, and so on, and outlining is performed according to each piece of data into which the image data was divided.
However, as described above, there are situations where converting the image to a vector image increases the overall amount of image data. The number of contour points increases particularly with characters that have complex shapes, and thus the increase in the data amount is especially prominent in cases where such characters are numerous. Although reducing the number of contour points can be considered here, doing so risks altering the shape of the character, and thus such a method is not favorable.